Abstract An experimental program was carried out to verify theoretical predictions of competitive effects exerted by nondisplaceable organic compounds on the uptake of TCE by activated carbon. Experimental findings were consistent with isotherm sensitivity analyses and thermodynamically based competitive adsorption model predictions. At low loadings of both trichlorobenzene and a natural humic acid, the most significant effect of preloading was to reduce the number of high-energy sites available to TCE. The loss of these sites caused a significant reduction in the site-energy heterogeneity and reduced the extent of adsorption in the low-concentration region. At higher levels of preloading, further changes in the site-energy heterogeneity were small, and uptake was reduced by a roughly equal percentage across a wide range of equilibrium concentrations, suggesting the possibility of a pore blockage (in the case of humic acid) or pore filling (in the case of TCB) mechanism. Measurements of adsorbent surface area and pore volume confirmed that observed reductions in TCE uptake by preloaded carbon were associated with changes in the physical characteristics of the adsorbent. However, reductions in adsorbent surface area could only account for a significant fraction ofthe observed reduction in TCE uptake when either the amountpreloaded was high or the TCE concentration was high, increasing the ability of TCE to compete for adsorption sites.